Electric heating apparatus



Sept 1, 1925.

L. C. GRANT ELECTRIC HEATING APPARATUS Filed Dec. 22, 1924 Patented Sept. 1, 1925.

UNI'TED STATE S PATENT OFFICE.

LEWIS ooLIN GRANT, or Nnwcn-srLn-ur-oN-rizNE, ENGLAND, AssIe oR To ELEC- TRICAL IMPROVEMENTS LIMITED, or NEWCASTLE-UPON-TYNE, ENGLAND, A.

BRITISH COMPANY.

ELECTRIC HEATING AYPARATUS.

Application filed December 22, 1924. Serial No. 757,567.

To all whom it may concern Be it known that I, LEWIS COLIN GRANT, a subject of the King of England, and residing at Newcastle-upon-Tyne, in the county of Northumberland, England, have invented certain new and useful Improvements in Electric Heating Apparatus, of

which the following is a specification.

This invention relates to heating apparatus employing the principle of' electrical induction and has more particular reference to electric heating apparatus for smelting purposes. In such apparatus it is'often advantageous to generate the heat for melting either directly in the body to be melted or as near as possible to it, and it is then desirable to use a comparatively high frequencyin order to transmit the electric energy economically to the heater.

The present invention has for its object to eifect improvements in such apparatus, whereby a high efliciency is obtained more especially in cases where high frequency currents are employed. It is to be under- 2 stood, however, that the invention is also applicable to cases where a medium or comparatively low frequency is required.

In the apparatus according to this invention a thermionic or other electrical valve circuit is employed to generate the currents supplied to an inductor coil for heating purposes. The inductor coil may itself form .part of the oscillatory circuit used for determining the frequency of the currents generated by the valve or Valves. Preferably two valves or banks of valves are provided in the generating circuit when an alternating current supply is used and are so arranged as to utilize both halves of the alternating power wave. The anode and grid circuits of the valve or valves may be cou- .pled together either electrostatically or electromagnetically as for example by means of an autotransformer, or alternatively the valves may be excited by means of a drive oscillator, which may or may-not consist of electrical valves.

The invention may be'carried into practice in various ways but a preferred arrangement according thereto is illustrated diagrammatically in F igure 1 of the accompanying drawings, a modified form of this arrangement being shown in Figure 2.

In the arrangement shown in Figure 1 erated. The coil of the secondary winding D being connected respectively to the anodes of the two banks of valves A B, thus utilizing both halves of the alternating power wave. Two choke coils D D are provided, one between each-set of anodes and the corresponding.

end of the secondary winding D, to prevent high frequency energy from the valves from passing into the transformer D D, and a condenser D is also connected across the winding D to short circuit any parasitic waves which may pass through the choke coils D D"-. Each set of ,anodes is also connected through a condenser E or E to a common wire leading to one of theoutput terminals E The grids of the valves are connected through a gridleak resistance F and condenser F to the other output terminal F The .two output terminals E F are connected together through a tuning condenser G and coil H in parallel, which determine the time constant of thecircuit and therefore also the fre uency'of the currents genis provided with a variable tapping H connected to the filament circuits of the valves.- This coil H thus acts as an auto-transformer, and is itself utilized as the heating inductor coil. It will be understood however that a separate inductor coil may be employed and may be connected across the two output terminals E F The apparatus operates in the followin manner. When the filaments are lighted and the high tension supply is applied to the anodes, the anode potential will rise and will cause a current to flow through the coil H and th valves. This causes flux and potential variations in the circuit which are reflected on the grid circuits of the valves,

so that the anode and grid circuits operate I current is thus generated, the frequency of which is dependent upon the time constant of the tuning coil H and the tuning condenser G. i

The single coil H, which acts as an autotransformer, may be replaced by two electromagnetically coupled coils, if desired, and such an arrangement is illustrated in Figure 2. This arrangement is largely identical with that of Figure 1, similar reference letters being employed for similar parts in the two figures, and only those parts .which differ from Figure 1 will be described. The output terminal F is in this arrangement connected to the filament circuits instead of to the grid circuits, and the lower ends of each of the two electromagnetically coupled coils H and H which replace the c011 H,

are connected to this output terminal F The upper end of the coil H is connected to the output terminal E and to the anodes, whilst th upper end of the coil H is connected through a variable tapping H to the grids of the valves, a condenser H being connected across from the tapping H to the output terminals F With this arrangement, the operation of which will be readily understood from the description given with reference to Figure- 1, the coil H may be utilized as the heating inductor coil or a separate inductor coil connected across the output terminals E F may be employed, if desired.

The employment of valves accordmg t0 the invention for generating the heating currents makes it ossible so to arrange the impedances in t e circuits that maximum efiiciency is obtainable.

It will be understood that the apparatus described and the modifications thereof have been given by way of example only and that other arrangements of circuits, wherein the oscillating currents are generated by means of thermionic or other electrical valves, may be employed without. departing from the scope of the invention.

What I claim as my invention and desire to secure by Letters Patent is 1. An electrical heating apparatus including in combination an inductor coil, and an electrical valve circuit which generates the currents supplied to the inductor coil for heating purposes.

2. An electrical heating apparatus including in combination an inductor coil, at least one thermionic valve for generating the currents supplied for heating purposes to the inductor coil, sources of current for the anode'and filament circuits of the valve, and tuning apparatus for determining the frequency of the currents generated by the valve.

3. An electrical heating apparatus including in combination an inductor coil, at least one electrical valve for generating the currents supplied for heating purposes to the inductor coil the necessary sources of ourrentfor the valve, and tuning apparatus of which the inductor coil forms part whereby the frequency of the currents generated by the valve is determined.

a. An electrical heating apparatus includ ing in combination an inductor coil, two banks of electrical valves which generate. the currents supplied for heating purposes to the inductor coil, each bank comprising at least one valve, a source of alternating current, means for connecting the valves to the source of current whereby both halves of the alternating power wave are utilized, and tuning apparatus for determining the frequency of the currents generated by the valves.

5. An electrical heating apparatus including in combination an inductor coil, two banks of electrical valves which generate the currents supplied for heating purposes to the inductor coil, each bank comprising at least one valve, a source of alternating current, means for connecting the valves to the source of current whereby both halves of the alternating power wave are utilized and tuning apparatus of which the inductor coil forms part whereby the frequency of the currents generated by the valves is determined.

6. An electrical heating apparatus includ-' ing in combination an inductor coil, at least one thermionic valve for generating the currents supplied for heating purposes to the inductor coil, sources of current for the anode and filament circuits of the valve, and electromagnetically coupled tuning apparatus for the anode and grid circuits.

7 An electrical heating apparatus includ- 7 ing in combination an inductor coil, at least one thermionic valve for generating the currents supplied for heating purposes to the inductor coil, sources of current for .the

anode and filament circuits of'the valve,

and tuning apparatus for the anode and grid circuits wherein a single coil acts as an auto-transformer for coupling the two circuits. together.

8. An electrical heating appartus including in combination an inductor coil, at least one electrical valve for generating the currents supplied for heating purposes to the inductor oil the necessary sources of current for t e valve, and tuning apparatus of which the inductor coil forms part whereby the frequency of the currents generated by the valve is determined, the inductor coil being arranged to act as an auto-transformer for coupling together the individual circuits of the valve. Y

9. An electrical heating apparatus including in combination an inductor coil, two banks of thermionic valves which generate the currents supplied for heating purposes to the inductor coil, a source of alternating termined, the inductor coil being arranged current, means for connecting the valvesto to act as an auto-transformer for coupling the source of current whereby both halves together the anode and grid'circuits of the 10 of the alternating power wave are utilized, valves.

and tuning apparatus of which. the inductor In tln o y wherepf I have signed my coil forms part whereby the frequency of, name to thls p the currents generated by the valves is. de- LEWIS COLIN GRANT. 

